Life History of Hemlock Woolly Adelgid, Adelges tsugae Annand, on Eastern Hemlock, Tsuga canadensis (L.) Carriere, in the Southern Appalachians and Assessment of Egg Releases of Sasajiscymnus tsugae (Sasaji and McClure) for Its Management
Date of Award
Master of Science
Entomology and Plant Pathology
Jerome F. Grant
Paris L. Lambdin, David S. Buckley, James R. Rhea
Studies were conducted in 2005 and 2006 at Baxter Orchard, Great Smoky Mountains National Park, Tennessee to optimize survival of Sasajiscymnus tsugae (St) (Sasaji and McClure) released as eggs on eastern hemlock, Tsuga canadensis (L.) Carriere, for biological control of Adelges tsugae (HWA) Annand. Studies investigated annual abundance and seasonality of HWA lifestages, weekly field and laboratory survival of St, and survival of St egg cohorts of various ages and densities. HWA was determined to be bivoltine on eastern hemlock in Tennessee with an aestivation period between July and October. Lifestages preferred as food by St were present from February through June with peak abundance ca. late March. Weekly survival of St placed in the field and laboratory as eggs was investigated. Less than 10% of St eggs placed in the field between 8 February to 22 March survived because of freezing field temperatures. Survival rose to 30-40% on 30 March and persisted at that level until 7 June, when survival decreased below 10% due to scarcity of food. Studies were conducted to investigate the effect of St egg density on survival of St. Four densities of St eggs (50, 100, 150, and 200 eggs/container) were placed in the field and laboratory. In the laboratory, survival was higher for lower densities of St eggs, implying cannibalism increases with density. Three egg age classes (0-2, 3-5, and 6-8 days old) were used to test the effect of St egg age on survival. St in field cages showed poor survival, likely due to freezing temperatures. However, the oldest (6-8 day) age class showed significantly greater survival in the field than the younger age classes. The two oldest age classes showed significantly greater survival than the youngest (0-2 day) age class in the laboratory. Results of multiple studies over two years support the release of St eggs to enhance biological control efforts against HWA. Studies showed St established as eggs in the field could successfully develop into adults. Survival of St from egg releases is highest when St eggs are released between late March and May, in low densities, and in older age classes.
Deal, Isaac K., "Life History of Hemlock Woolly Adelgid, Adelges tsugae Annand, on Eastern Hemlock, Tsuga canadensis (L.) Carriere, in the Southern Appalachians and Assessment of Egg Releases of Sasajiscymnus tsugae (Sasaji and McClure) for Its Management. " Master's Thesis, University of Tennessee, 2007.